Preparing explosive composition having precipitated salt mix

ABSTRACT

A CASTABLE BLASTING AGENT IS PROVIDED WHICH REMAINS IN A SOLIDIFIED FORM BELOW A PREDETERMINED DESIRED STABILITY TEMPERATURE. THE BLASTING AGENT IS PRODUCED BY MIXING A HEATED AQUEOUS SOLUTION OF AN INORGANIC OXIDIZING SALT MAINTAINED AT A TEMPERATURE ABOVE THE DESIRED PREDETERMINED TEMPERATURE, WITH PARTICULATE EXPLOSIVE ADDITIVES, E.G. INORGANIC OXIDIZING SALTS, FUELS, SENSITIZERS AND THE LIKE, AND COOLING THE MIX TO SOLIDIFY THE SAME IN SHAPED OR CAST FORM.

United States Patent once Patented June 5, 1973 3,737,350 PREPARING EXPLOSIVE COMPOSITION HAVING PRECIPITATED SALT MIX Charles H. Grant, Midland, Mich., assiguor to The Dow Chemical Company, Midland, Mich.

No Drawing. Continuation of application Ser. No. 873,119, Oct. 31, 1969. This application Jan. 31, 1972, Ser. No. 222,354

Int. Cl. C0611 19/00 US. Cl. 149-17 4 Claims ABSTRACT OF THE DISCLOSURE A castable blasting agent is provided which remains in a solidified form below a predetermined desired stability temperature. The blasting agent is produced by mixing a heated aqueous solution of an inorganic oxidizing salt maintained at a temperature above the desired predetermined temperature, with particulate explosive additives, e.g. inorganic oxidizing salts, fuels, sensitizers and the like, and cooling the mix to solidify the same in shaped or cast form.

This is a continuation of application Ser. No. 873,119, filed Oct. 31, 1969, now abandoned.

BACKGROUND OF THE INVENTION Various castable blasting agents are well known in the art. They are presently prepared by one of four general methods. Melt blasting agents are prepared by melting one or more inorganic oxidizing salts, or self-explosives, e.g. TNT, and while molten, adding thereto other constituents required to make an effective blasting agent, e.g. fuels, air voids, etc., the resultant mixture thereafter being allowed to cool to solidify in shaped or cast form. Exemplary of a melt blasting agent is that taught in Canadian Pat. No. 803,945, issued Jan. 14, 1969.

A second method for producing a castable solidified blasting agent comprises preparing a blasting agent containing particulate and liquid phases and incorporating therein a setting agent which sets the blasting agent to a solid shaped or cast form. Exemplary of such a method and blasting agent is taught in US. Pat. 3,326,734.

A third method for preparing a cast blasting agent is to employ a sufficient quantity of a suitable polymeric material in a liquid containing blasting agent to form a castable blasting agent.

Still another method for preparing castable solidified blasting agents comprises saturating a suitable liquid with at least one inorganic oxidizing salt at an elevated temperature to provide a fluid or mobile system, optionally mixing other constituents into the fluid system, and cooling the mixture, whereupon reprecipitation of a portion of the dissolved salt from solution produces a solidified shaped or cast form. Exemplary of such a blasting agent is taught in US. Pat. No. 3,390,029.

The present invention pertains to a solidified blasting agent in shaped or cast form which is characterized as maintaining said form when subjected to heat up to a predetermined desired stability temperature. A reprecipitation method is employed to prepare the castable explosive. Advantages of the novel blasting agent and method for preparing the same over those prepared by melt, setting or polymeric methods include better dimensional stability at selected predetermined elevated temperatures, maintenance of integrity at elevated temperatures, absence of difficulties encountered when employing melt temperatures during manufacture thereof and the like.

SUMMARY or THE INVENTION The present invention concerns a blasting agent in a cast or shaped solidified mass and to the method of producing the same. The blasting agent comprises water, a fuel and an inorganic oxidizing salt, at least a portion of said inorganic oxidizing salt being present as a continuous matrix formed upon the precipitation of a salt from an aqueous solution thereof which binds the constituents to form a solidified mass in shaped or cast form. The blasting agent is produced by mixing all the constituents together in the presence of a sufficient quantity of a heated aqueous solution, maintained at a temperature sufficiently above a desired predetermined stability temperature, and having dissolved therein a sufiicient amount of at least one inorganic oxidizing salt, such that upon cooling the mixture a sufiicient quantity of said dissolved salt precipitates from said solution at said desired predetermined stability temperatures to form a continuous solid matrix binding the constituents together to form a solidified blasting agent in shaped or cast form.

Stability temperature as employed herein means the maximum temperature below the melting point of the lowest melting constituent present in a substantial amount at which the blasting agent of the present invention remains a substantially solid mass.

DETAILED DESCRIPTION OF THE INVENTION Percent by weight Range Preferred At least pne inorganic oxidizing salt About 30 to About 55 to a sufficient proportion of which is about 95. about 75.

in a crystalline form, obtained by precipitating a portion of said salt from a heated aqueous solution of said salt(s Water dispersible organic luel. About 0 to 20 About 2 to 10.

. About .5 to About 2 to Water about 10. about 4.

Particulate metal 0 to about 60-.." About 15 to about 30.

Thickening agent About 0 to About .4 to about 10. about 12.

A sufiicient volume of gaseous voids is incorporated into the blasting agent to lower the density thereof to a value at which the blasting agent can be readily exploded with a conventional initiator. A density ranging from about .90 to 1.75 gm./cc. is desired while a density of from 1.05 to 1.50 gm./cc. is preferred.

Optionally other constituents which may be included are ingredients which aid in the manufacture of the blasting agent, e.g. surfactants, dispersants and the like, and agents which aid in providing extended periods of shelf life, e.g. inhibitors for the particulate metal, thickening agents and the like.

Inorganic oxidizing salts which may be employed herein are particulate forms of alkaline earth metal, alkali metal and ammonium nitrates, perchlorates, chlorates and various mixtures thereof. For example, ammonium nitrate, sodium nitrate, barium nitrate, calcium nitrate, potassium nitrate, ammonium perchlorate, sodium perchlorate and other like inorganic oxidizing salts and mixtures thereof known in the explosives art can be employed. Exemplary of such salts are the particulate form of those salts taught at column 4, lines 64-73 and column 5, lines 63-70 of US. Pat. No. 3,462,324, said teachings being specifically incorporated herein by reference. In the present invention a mixture of ammonium nitrate and sodium nitrate and/or calcium nitrate is preferred with ammonium nitrate being present in the major proportion based on the weight of the salts. The salts may be employed in any particulate form, prilled, crushed or the like. As indicated a portion of the salt is present in a crystalline form. The exact nature of the crystal structure is not known, however, it is prepared during the novel method of preparing the novel blasting agent as more specifically set forth hereinafter. The crystals are formed upon the precipitation of the salt from an aqueous solution of the salt when it is cooled. The crystalline form provides a matrix which binds the other constituents together to form a solidified mass.

Preferably, the organic fuel solvent is liquid at room temperature. Examples of fuel solvents which can be employed are various glycols, alcohols, amines, amides, for example, formamide, ethylene glycol, propylene glycol, polyglycols, or glycerin can be employed. The organic fuel solvents preferably are dispersible, e.g. miscible or soluble, in water. Examples of such compounds include organic compounds which contain at least one functional group of =0, OH, :NH, NH EN, :8, or -SH.

Particulate metals which can be employed herein are those metals which oxidize under explosive conditions to produce heat and gas expansion. Particulate metals known in the explosive are suitable for use in the present invention. Included by way of example are, aluminum, magnesium, aluminum-magnesium alloys, ferro silicon, ferro-phosphorous, iron, boron, vanadium, chromium, thorium, titanium, tungsten, and mixtures of alloys containing one or more metals. The particulate metal can vary in size. The exact particle size range will depend on various properties of the particular metal employed, the sensitivity and power of the blasting agent desired and the like. For example, in order that the metal will readily enter into the explosive reaction heavy metals such as ferrophosphorous, iron and the like must ordinarily be provided in a finely divided size, i.e. -325 mesh. For light metals, aluminum, magnesium alloys thereof and the like a coarser size can be employed, e.g. ranging from 4 to about 200 mesh. Although coarser light metal can be employed the present invention is not limited thereby and fine light metals, e.g. 200 mesh can also be used in varying amounts. As indicated the exact size range of metal will depend on the metal, and the characteristics of the blasting agent which are desired. These properties are well known to those skilled in the explosive art. For an example of the type and size distribution of metal which can be employed in the composition and method of the present invention, reference is made to U.S. Pat. Nos. 3,307,986 and 3,432,371. The teachings of these patents are pertaining to the particulate metals employed in the compositions and methods of the inventions therein described are specifically incorporated herein by reference.

Thickening agents employed herein are any of those polymeric water soluble materials well known in the explosives art for thickening and/or gelling aqueous solutions of inorganic oxidizing salts which contain a water miscible organic fuel solvent. Suitable thickeners include polysaccharides, partially synthetic polymers and synthetic polymers. Exemplary of suitable thickening agents are those taught in U.S. Pat. Nos. 3,446,681; 3,400,026 (column 5, lines 25-63); 3,355,336 and 3,190,977 (column 4, line 50 through column 5, line 12). The teachings of said patents are specifically incorporated herein by reference.

Also included in the present composition is a sufficient amount of small gaseous voids to aid in the explosion of the blasting agent. The voids may be provided by incorporating gas bubbles in the blasting agent during manufacture, e.g. by agitation, with the aid of a bubble stabilizer, e.g. a material which prevents the small bubbles from coalescing, amphoteric surfactants such as salts or free acid forms of N-alkyl-beta-aminopropionic acid or N-alkyl-beta-irnino-dipropionic acid, solid under the trademark Diriphat. Thickening and gelling agents also aid in stabilizing the bubbles. In conjunction with gaseous bubbles or alternatively gaseous voids may be incorporated into the blasting agent by mixing therein discrete hollow gaseous containing particles. These particles may be made from such materials as glass, thermosetting resins, metals, clays and the like. Natural occurring void containing materials, e.g. cork, corn husks and the like can also be employed. Reference is made to U.S. Pat. No. 3,456,589, column 2, lines 34-42 for teachings related to hollow glass spheres which may be employed in the present invention. Other void containing materials which can be employed are taught in U.S. Pat. No. 3,101,288. The relevant teachings of said patents are specifically incorporated herein by reference.

Optionally, other constituents can also be employed in the composition of the present invention. For example various other surfactants and dispersing agents may be employed to aid in manufacturing the blasting agent. Various corrosion inhibitors may be incorporated into the composition to reduce the reactivity of the particulate metal to corrosion caused by other constituents in the mix, e.g. water. Examples of such inhibitors include mannitol and various phosphorous containing compounds such as taught in U.S. Pat. No. 3,113,059, the teachings thereof being specifically incorporated herein by reference.

The method for preparing the blasting in shaped or cast form comprises mixing the constituents herein before described with an aqueous solution at a temperature sufficiently above a desired stability temperature and having dissolved therein a sufiicient amount of at least one inorganic oxidizing salt that upon cooling the mixture a sufficient quantity of said dissolved salt precipitates from said solution at said desired stability temperature to form a matrix binding the constituents together forming a solidified mass, said constituents being provided in proportion effective to produce a blasting agent which is detonable with standard initiators known in the art, e.g. high pressure boosters and the like. The order of additions of the individual constituents to the mixture is not critical except that if the gaseous voids are to be incorporated in the blasting agent by agitation to form bubbles, this step is usually performed just prior to cooling the mixture to form the matrix.

A preferred method for preparing a blasting agent as defined herein having a stability temperature of about F., and the product of such process comprises:

maintaining a solution comprising (as parts by weight): At least one inorganic oxidizing salt 20-30 Liquid organic fuel 2-3 Water 2-3 Optionally metal corrosion inhibitor 0.1-1

at a temperature of about to 200 F. This solution contains substantially no solids. To this heated solution is added with mixing solid ingredients comprising additional particulate inorganic oxidizing salts 30-50 parts, and particulate metal, 0 to 60, preferably 15 to 30 parts with mixing while heating the mixture to about 200 to 210 F. The mixture is mixed for a sufiicient period of time to provide a soft thick homogenous slurry which is substantially free from lumps and conglomerates of solid particles. Preferably the solid constituents are mixed into the initial heated solution in the following manner. About one half of the remaining inorganic salt (15-25 parts) is added to the initial heated solution with mixing and heating the mixture to about 200-210 F. The mixture is mixed for a suificient period of time to break down any lumps and provide a thin slurry. To the thin slurry is then added the particulate metal while maintaining the mixture at a temperature of from about 200 to 210 F. The mixing is continued for a sufiicient period of time to break up any lumps. To this slurry of metal and solid inorganic oxidizing salts is then added the remaining inorganic oxidizing salt (25 parts) with mixing and heating to maintain the mixture at a sufiicent temperature (-200 F.) to provide a thick homogenous slurry. It has been found that if the mixture, following the addition of the particulate metal, contains foam 0r froth it is advantageous to add the remaining particulate inorganic oxidizing salt fast enough to cause lumping and dryness. This method of mixing will break the foam bubbles. The specific gravity of the thick homogenous slurry is about 1.45 to 1.55 gm./cc. The heat is lowered considerably or completely shut off at this point, while mixing of the slurry is continued. Gaseous voids are then incorporated into the mix by either agitating it sufliciently to whip air bubbles therein along with the addition of a bubble stabilizer and/or void containing materials are added to provide a final specific gravity of about 1.40 to 1.50 gm./cc. A thickening and/or gelling agent (0.1-1 parts) is then mixed into the slurry to hold the air bubbles, and/or other void containing materials and solid constituents in suspension until the blasting agent has cooled and solidified. The slurry at this point should still be at an elevated temperature, 195-200 F. The slurry can then be poured into preshaped molds or containers whereupon it is cooled to form a solidified mass. It has been discovered that the sensitivity of the blasting agents of the present invention to detonation can be increased by rapidly cooling the hot slurry to about room temperature, i.e. in 6-8 hours or faster, other sensitivity when it is cooled slowly, i.e. 24- 36 hours. The reason for this difference is not entirely understood but it may be related to the size and character of the crystalline form of the inorganic oxidizing salt which is precipitated from solution upon cooling.

EXAMPLE 1 Sodium nitrate 4 Ammonium nitrate Formamide 2.5 Water 2.5 Mannitol 0.25

The solution was heated in a turbine mixer, equipped with a steam jacket, to a temperature of 198 F. To the heated solution in the mixer was added parts crushed ammonium nitrate explosive grade prills (about 53 percent by weight being +100 mesh and the remainder 100 mesh US. Standard Sieve Series). The constituents were continually mixed with the turbine mixer running at a speed of 36 r.p.m. The mixture was heated to a term perature which ranged from about 200-208 F. The composition appeared as a thin slurry of the crushed nitrate in the solution. To the slurry was added 25 parts of atomized aluminum (about 72 percent by weight being +325 mesh and the remainder -325 mesh US. Standard Sieve Series), While the mixer was running at 18 r.p.m. The speed was increased to about 36 r.p.m. for about 1 minute to break up lumps in the mix. The composition was maintained at a temperature of about 200 F.208 F. Following the addition of the aluminum and mixing to remove lumps, 20 parts by weight of additional crushed ammonium nitrate was added to the composition while mixing at 12 r.p.m. The mixing of the composition was continued until the composition was softened to a thick homogenous slurry while maintaining the slurry at a temperature of about 200 F. The heat was then shut off and while still mixing at a speed of 12 r.p.m. 0.25 part of a partial sodium salt of N-lauryl-beta-iminodipropionic, a bubble stabilizer sold under the trademark Diriphat 160C was added and the mixing at 12 r.p.m. continued for about seconds. The speed was then increased to about 18 r.p.m. for another 30 seconds. While continuing the mixing at a speed of 18 r.p.m. about 1.2 parts of a mixture containing about 0.2 part guar gum, 0.2 part partially cross-linked guar gum dispersed in about 0.8 part of ethylene glycol, was added and the mixing continued at 18 r.p.m. for about 30 seconds. The slurry was then finally mixed at a speed of about 24 r.p.m. to allow the gums to hydrate and hold the air bubbles entrained by the bubble stabilizer. The final slurry was still at a temperature of about 196 F. Several 2 gaL-S gal. containers were filled with the slurry and the slurry allowed to cool and set up to a solidified mass.

The blasting agent prepared by the above method contains the following constituents as parts by weight:

Constituent: Parts by weight Ammonium nitrate (a portion forming the bending matrix and a portion in particulate The above composition has a stability temperature of about F. and a density of about 1.45 gm./cc.

The blasting agent prepared above was then tested in a standard underwater testing procedure. In this procedure the composition in the container was armed with a high density primer and the primer attached to a strand of high velocity detonating cord. The pails were sealed with a lid through which the cord extended. Water resistance was assured by a gasket sealing assembly at the opening where the cord came through the lid. The compositions were tested in a standard underwater test. In the testing, the cord was connected to an initiator and firing line and the composition was detonated in a body of water at about half the depth of a lake (pail placed at 42.5 feet beneath the surface of the water). The resulting pressure profile from the detonation was converted into electrical impulses by a piezoelectric gauge suspended in the water at the same level a known horizontal distance from the charge. The electrical impulses are recorded and converted to the corresponding pressures and from this the peak pressure, shock energy, bubble energy, the total energy based on weight, the total energy based on volume of the explosive were calculated by methods described in Underwater Explosives, R. H. Cole, Princeton University Press (1948). In the following examples and tables, peak pressure will be designated as PK, the shock energy as ESN, the bubble energy as Y, and the total energy based on Weight ET and total energy based on volume ETV.

As a comparison two self-explosives containing cast blasting agents widely employed in ammunitions were tested in a like manner. The two self-explosive containing compositions contained the following constituents as percent by weight:

The compositions of Mix 1 and Mix 2 are well known cast explosives known in the art as Minol-2-and Tritonal respectively. In each instance the density of the blasting agents and the underwater test data is set forth in the following Table II. The novel blasting agents prepared by the novel method taught herein are designated as Cast Mix while the two self-explosive containing compositions are designated Mix 1 and Mix 2, corresponding to the compositions set forth in Table I.

TABLE II Shot Den- Composition No. sity PK ESN Y ET ETV Mix 1 1 1. 605 4, 047 0. 698 0. 703 1. 402 2. 250 2 1. 608 4, 629 o. 756 o. 722 1. 478 2. 378

Mix 2 6 1. 622 3, 935 0. 769 0. 747 1. 516 2. 459 7 1. 583 3, 680 0. 659 0. 765 1. 425 2. 255

Cast mix 10 1. 446 3, 641 0. 756 0. 966 1. 723 2. 401 11 1. 445 3, 846 0. 806 0. 947 1. 753 2. 533

The blasting agent prepared by the method of the present invention showed greater total potential work as exemplified by E than either of the two self-explosive containing compositions. The peak pressure of the :blasting agent of the present invention compared favorably with the self-explosive mixes.

EXAMPLE 2 Another blasting agent was prepared in the following manner. A mixture containing 220 grams of ammonium nitrate prills, 60 grams of water and 3.3 grams of guar gum was heated to 200 F. To this mixture was then added about 78 grams of particulate ammonium nitrate, about 2.4 grams of fuel oil, 125 grams of particulate aluminum, and a small amount of Na Cr O mixing until a smooth slurry was formed. The mixture was then cooled whereupon a hard solidified blasting agent was formed.

What is claimed is:

1. A method for preparing a solidified blasting agent containing an inorganic oxidizing salt, a water soluble organic fuel, and water in shaped form which remains substantially solidified at a predetermined elevated stability temperature which is lower than the melting point of the lowest melting constituent in said blasting agent present in a substantial amount which comprises:

(a) mixing the constituents comprising said blasting agent with a suflicient quantity of a heated aqueous solution maintained at a temperature sufiiciently above said predetermined stability temperature and having dissolved therein a suflicient quantity of an inorganic salt that upon cooling the mixture a sufficient quantity of said dissolved salt precipitates from 8 said solution at said stability temperature to form a substantially continuous matrix binding the constituents together to form said blasting agent in solidified form, and

(b) cooling said mixture to precipitate said salt forming a solidfied blasting agent.

2. A method for producing a blasting agent in shaped or cast form and containing an inorganic oxidizing salt, water, a liquid water dispersible organic fuel, particulate metal fuel, and a thickening agent which has a stability temperature of about F. which comprises:

(a) heating a solution comprising, as parts by weight:

(1) 2030 parts of an inorganic oxidizing salt; (2) 2-3 parts liquid Water dispersible organic fuel; (3) 2-3 parts H O to about to 200 F.;

(b) mixing into said solution from about 3050 parts additional inorganic oxidizing salt and about 15 to about 30 parts of a particulate metal fuel, and heating the mixture to from about 200 to about 210 F. to produce a heated slurry mixture having a density ranging from about 1.45 to about 1.55 gm./cc.;

(c) agitating the mixture sufiiciently to whip air bubbles into the mix, to provide a mixture having a density ranging from about 1.40 to 1.50 gm./cc.;

(d) adding from about 0.1 to about 1 part of a thickening agent into said mixture with continual mixing; and

(e) cooling the mixture to about room temperature to solidify the mixture.

3. The method as defined in claim 2 wherein the mixture is placed in molds prior to cooling.

4. The method as defined in claim 2 wherein the mixture is cooled from the temperature of from about 200 to about 210 F. to room temperature in less than about 8 hours.

References Cited UNITED STATES PATENTS 2,589,532 3/1952 Byers et al. 1495 X 3,009,801 12/1961 Blackwell 149-5 3,370,537 2/1968 Tepper 14917 X 3,378,415 4/1968 Grifiith 149'-17 3,421,954 1/1969 'Falconer 149--17 3,497,404 2/1970 Hiltz 149-17 STEPHEN J. LECHERT, JR., Primary Examiner U.S. Cl. X.R. 

